a) Field of the Invention
This invention relates to procedures and apparatus useful for safely destroying toxic chlorine- and arsenic-containing chemicals, and toxic chlorine- and sulfur-containing chemicals, e.g., obsolete chemical warfare agents.
b) Description of the Prior Art
In recent years with the global emphasis on the reduction of the huge stockpile of chemical warfare agents, the art has been confronted with the problem of safely destroying and disposing of a variety of obsolescent chemical warfare agents, e.g., mustard gas and Lewisite.
Large quantities of chemical warfare agents, in various forms, are contained in a wide spectrum of munitions ranging from tactical ordnance to ballistic missiles, while equally large quantities are found in storage vessels with capacities ranging from a few grams to several tonnes. The problem of treatment and disposal is, therefore, severely complicated, not only by the extreme toxicity of quite infinitesimal quantities of these agents, but also by the need to simplify their recovery and to minimize the number of transfer and handling steps.
Where the technique of incineration is permitted, certain of these agents, including mustard gas and the nerve gases, may be totally destroyed through thermal oxidation, since the products of combustion, e.g., sulfur dioxide, may be readily contained and prevented from escaping to the atmosphere.
On the other hand, the Lewisites, [i.e., dichloro(2-chlorovinyl)arsine, bis(2-chlorovinyl)chloroarsine and tris(2-chlorovinyl)arsine], which comprises approximately 36 weight percent arsenic, upon combustion produce the highly toxic arsenic trioxide. Under conditions normally experienced in incinerator operation, it is extremely difficult to limit the release of this contaminant to the atmosphere at acceptably low rates.
Numerous chemical neutralization techniques have been proposed in the literature based on an alkaline oxidation, e.g., as taught in Canadian Patent No. 304,110 patented Sep. 23, 1990 by C. D. Carpenter. A large proportion of these techniques are based on hydrolysis of the Lewisite I in an aqueous alkaline medium. The reaction involved may be represented by the equation: EQU Cl--CH.dbd.CH--AsCl.sub.2 +6NaOH.fwdarw.Na.sub.3 AsO.sub.3 +CH.tbd.CH.uparw.+3NaCl+3H.sub.2 O (1)
Although the hydrolysis approach, especially at somewhat elevated temperatures, is capable of effectively destroying virtually all of the principal Lewisite specie, known as Lewisite I, the associated species, Lewisite II and Lewisite III (previously generically-termed "the Lewisites") are considerably more resistant to hydrolysis and will, to a considerable extent survive this treatment. The secondary species, though milder vesicants than the principal analogue, are nonetheless toxic and cannot be tolerated as a component of the reaction products.
Another undesirable feature of the hydrolysis procedure is the formation of a trivalent arsenic compound, sodium arsenite which represents one of the most toxic forms of arsenic. Moreover, since this product is extremely soluble, some considerable difficulty is encountered in achieving its secure, permanent disposal.
A second popular approach suggested in the literature involves oxidation of the Lewisite with the aid of some oxidizing agent, e.g., sodium hypochlorite (NaOCl), chlorine (Cl.sub.2), hydrogen peroxide (H.sub.2 O.sub.2) or nitric acid (HNO.sub.3).
Although complete oxidation may be possible with the nitric acid, reagents, e.g., hypochlorites and peroxides were, under the conditions investigated, found to be capable of only partial oxidation in accordance with the following reactions: EQU 2(Cl--CH.dbd.CH--AsCl.sub.2)+2NaOCl+4NaOH.fwdarw.2(Cl--CH.dbd.CH--AsO.sub.3 H.sub.2)+6NaCl (2) EQU Cl--CH.dbd.CH--AsCl.sub.2 +H.sub.2 O+H.sub.2 O.sub.2 .fwdarw.Cl--CH.dbd.CH--AsO.sub.3 H.sub.2 +2HCl (3)
In each instance, a final product of the reaction is a chlorovinyl arsonic acid which, though less noxious than the original Lewisite, is nevertheless highly toxic and represents a significant final disposal problem.
It should be noted that products analogous to the arsonic acid produced by the oxidation of Lewisite I are derived from similar oxidations of Lewisite II and Lewisite III and that these constitute comparable disposal problems.